1. Field of the Invention
The present invention relates to a method of manufacturing a thin-film magnetic head having at least an inductive-type magnetic transducer for writing.
2. Description of the Related Art
Improvements in the performance of a thin-film magnetic head have been sought since a surface recording density of a hard disk drive has been improved. A composite thin-film magnetic head having a structure in which, a recording head having an inductive-type magnetic transducer for writing and a reproducing head having a magnetoresistive (hereinafter referred to as MR) element for reading are stacked, is widely used as the thin-film magnetic head. The MR element includes an AMR element using an anisotropic magnetoresistive (hereinafter referred to as AMR) effect and a GMR element using a giant magneto resistive (hereinafter referred to as GMR) effect. The reproducing head using the AMR element is called an AMR head or simply an MR head, and the reproducing head using the GMR element is called a GMR head. The AMR head is used as a reproducing head whose surface recording density is over 1 gigabit per square inch, and the GMR head is used as the reproducing head whose surface recording density is over 3 gigabit per square inch.
The AMR head comprises an AMR film having the AMR effect. The GMR head has a structure identical to the AMR head except that a GMR film having the GMR effect is used in place of the AMR film. However, when the same external magnetic field is applied, the GMR film exhibits greater change in resistance than the AMR film. As a result, the GMR head can increase the reproduction output in the order of three to five times the AMR head.
In order to improve the performance of the reproducing head, a method of replacing the AMR film with a material having better magnetoresistive sensitivity such as the GMR film as the MR film, a method of making an appropriate pattern width of the MR film, especially the MR height and other methods are employed. The MR height is a distance between an end of the MR element on the air bearing surface side to an end thereof on the other side, and it is controlled by a polishing amount in processing the air bearing surface. The air bearing surface, here, is a surface of the thin film magnetic head facing a magnetic recording medium, and is called a track surface as well.
On the other hand, improvements in performance of a recording head have been desired while performance in a reproducing head has improved. A factor which determines the performance of the recording head is a throat height. The throat height is a length of a pole between the air bearing surface and an edge of an insulating layer which electrically separates a thin-film coil for generating magnetic flux. The throat height is desired to be optimized in order to improve the performance of the recording head. The throat height is controlled by a polishing amount in processing the air bearing surface.
To improve a recording density among the performance of the recording head, a track density of the magnetic recording medium needs to be increased. In order to achieve such an increase, a recording head with a narrow track structure needs to be realized in which a width of the top and bottom poles on the air bearing surface, which are formed on top and bottom sandwiching a write gap, is reduced from the order of some microns to sub-microns. Semiconductor process techniques are employed to achieve the narrow track structure.
A method of manufacturing the composite thin-film magnetic head as an example of the methods of manufacturing the thin-film magnetic head of the related art will be described by referring to FIG. 27 through FIG. 32.
As shown in FIG. 27, in this manufacturing method, an insulating layer 102 made of, for example, aluminum oxide (Al2O3; hereinafter referred to simply as “alumina”) of about 5 μm to 10 μm in thickness is deposited on a substrate 101 made of, for example, altic (aluminum oxide and titanium carbide; Al2O3.TiC). A bottom shield layer 103 for a reproducing head is formed on the insulating layer 102. A shield gap film 104 is formed on the bottom shield layer 103 by, for example, sputter-depositing alumina with 100 nm to 200 nm in thickness. An MR film 105 of tens of nanometers in thickness for making up the MR element for reproduction is formed on the shield gap film 104, and patterned in a desired shape through photolithography with high precision. Next, after forming lead layers (not shown) on both sides of the MR film 105 as an extraction electrode layer which is electrically connected to the MR film 105, a shield gap film 106 is formed on the lead layer, the shield gap film 104 and the MR film 105, and then the MR film 105 is buried in the shield gap films 104 and 106. Further, a top shield-cum-bottom pole (hereinafter referred to simply as a bottom pole) 107 made of magnetic materials, such as ferronickel (NiFe; hereinafter referred to simply as “permalloy” (trade name)) used for both reproduction and recording heads is formed on the shield gap film 106.
As shown in FIG. 28, a write gap layer 108 made of an insulating material, such as alumina, is formed on the bottom pole 107, and a photoresist film 109 in a desired pattern is formed on the write gap layer 108 through photolithography with high precision. Next, a thin-film coil 110 for an inductive-type recording head made of, for example, copper (Cu) is formed on the photoresist film 109 by, for example, plating. A photoresist film 111 in a desired pattern is formed covering the photoresist film 109 and the thin-film coil 110 through photolithography with high precision. Next, the photoresist film 111 is subjected to a heat treatment at a temperature of, for example, 250° C. to have turns of the coil 110 insulated from each other.
As shown in FIG. 29, an opening 108a is formed by partially etching the write gap layer 108 in a position behind the coil 110 (right-hand side in FIG. 29) to expose part of the bottom pole 107 in order to form a magnetic path. A film of a magnetic material with a high saturation magnetic flux density, such as permalloy, is formed by an electrolytic plating, covering the exposed surface of the bottom pole 107, and the photoresist film 111 and the write gap layer 108. The plated film formed of permalloy is selectively etched by ion milling using a mask (not shown) formed of a photoresist film having a prescribed planar shape, to thereby form a top yoke-cum-top pole (hereinafter referred to as a top pole) 112. The top pole 112 has, for example, such a planar shape as shown in FIG. 32, which will be described hereinafter, and includes a yoke 112a and a pole tip 112b. The top pole 112 has a contact with the bottom pole 107 in the opening 108a being magnetically coupled. Next, after both the write gap layer 108 and the bottom pole 107 are partially etched about 0.5 μm by ion milling using part of the top pole 112 (the pole tip 112b) as a mask (see FIG. 31), an overcoat layer 113 is formed of a material, such as alumina, on the top pole 112. The thin-film magnetic head is completed after a track surface, that is, air bearing surface 120 of the recording head and reproducing head is formed by machining or polishing.
FIG. 30 through FIG. 32 show a completed configuration of the thin-film magnetic head. FIG. 30 shows a cross-sectional view of the thin-film magnetic head orthogonal to the air bearing surface 120, FIG. 31 is an enlarged cross-sectional view of the pole in parallel to the air bearing surface 120, and FIG. 32 is a plan view. FIG. 29 is a cross sectional view taken along the line XXIX—XXIX in FIG. 32. Illustrations of the overcoat layer 113 and the like are omitted in FIG. 30 to FIG. 32. The thin-film coil 110 shown in FIG. 32 is only the outermost periphery portion thereof, and the photoresist film 111 shown therein is only the outermost end thereof.
In FIG. 30 and FIG. 32, “TH” stands for throat height, and “MR-H” stands for MR height. In both of these figures, “TH0 position” is the position of the end of the photoresist layer 111, which serves as an insulating layer for electrically insulating the thin-film coil 110, located nearest to the air bearing surface 120. This is the reference position in defining a throat height, that is, a throat height zero position. Meanwhile, “MRH0 position” is the position of the end of the MR film 105 which is farthest from the air bearing surface 120, i.e. an MR height zero position.
Other than the throat height (TH) and the MR height (MR-H), one of the factors that determine the performance of the thin-film magnetic head is an apex angle (θ) shown in FIG. 30. The apex angle θ is the average tilt angle of the slope of the photoresist film 111 located on the side closer to the air bearing surface 120.
As shown in FIG. 31, a structure in which the write gap layer 108 and the bottom pole 107 are both partially etched in a self-aligned manner to the pole tip 112b of the top pole 112 is called a trim structure. The trim structure prevents an increase in the effective track width, which would otherwise be occurred through expansion of the magnetic flux generated during writing of a narrow track. In FIG. 31, “P2W” represents a width of the portion with the trim structure (hereinafter referred to simply as a “pole tip 200”), that is, a pole width or a “track width”. In the same figure, “P2L” represents the thickness of the pole tip 112b forming part of the pole tip 200, that is, the length of the pole. As shown in FIG. 31, lead layers 121 as an extraction electrode layer being electrically connected to the MR film 105 is provided on both sides of the MR film 105. However, an illustration of the lead layers 121 is omitted in FIG. 27 to FIG. 30.
As shown in FIG. 32, the top pole 112 is composed mostly of the yoke 112a. The top pole 112 includes the pole tip 112b having an almost uniform width as the pole width P2W as well. At a coupling portion of the yoke 112a and the pole tip 112b, an outer periphery of the yoke 112a has an angle α against a surface parallel to the air bearing surface 120. At the above coupling portion, an outer periphery of the pole tip 112b has an angle β against the surface parallel to the air bearing surface. Here, α is, for example, about 45 degrees, and β is 90 degrees. As described above, the pole tip 112b serves as a mask for forming the trim structure of the pole tip 200. As can be seen from FIG. 30, the pole tip 112b extends over the flat write gap layer 108, while the yoke 112a extends over a coil portion (hereinafter referred to as an “apex portion”) covered with the photoresist film 111 and raised like a hill.
The characteristics of the structure of the top pole is disclosed in detail in, for example, Unexamined Patent Application Publication No. Hei 8-249614. This publication discloses a top pole with a structure where the width of the portion located behind the TH0 position (the side farther away from the air bearing surface 120) is gradually widened.
As the pole width P2W of the pole tip 200 defines the recording track width on a recording medium, it is required that the pole tip 200 is formed with high precision and that the pole width P2W is reduced in order to increase recording density. If the pole width P2W is too great in value, a phenomenon in which data is written also to the area adjacent to a predetermined recording track area on the recording medium, that is, a side erase phenomenon, occurs, thereby preventing improvement in recording density. Therefore, it is important to simultaneously reduce the pole width P2W of the pole tip 200 and have such a pole width P2W that is constant throughout the thickness direction (vertical direction in FIG. 31) and the length direction (horizontal direction in FIG. 30).
The top pole 112 can be formed by a wet process, such as a frame plating, or by a dry process in which a plated film formed of, for example, permalloy is selectively etched and patterned by ion milling, as described above.
However, the applicants have confirmed that the ion milling brings about the following problems. For example, when ion beam is irradiated from a direction substantially perpendicular to the surface of the plated film (a direction at an angle of 0 degree to 30 degrees to the perpendicular line to the surface of the plated film), the etching product generated in etching is reattached to the unetched portion, whereby the width of the pole tip 112 is partially increased from the designed value. On the other hand, when, for example, ion beam irradiation is performed from a direction substantially parallel to the surface of the plated film (a direction at an angle of 50 degrees to 70 to the perpendicular line to the surface of the plated film), the above-described reattachment of the etching product can be prevented. However, the etching amount is increased as the process proceeds, leading to partial decrease in width of the pole tip 112b from the designed value. When the pole tip 200 is formed by ion milling under the latter conditions above in particular, the pole width P2W will be inconstant as shown in FIG. 33.
In the related art method, since the photoresist pattern obtained by selectively exposing to light the photoresist film formed on the plated film is used as a mask for patterning the plated film of permalloy. This deteriorates precision in forming the mask due to adverse effects of the light reflected from the surface of the underlying permalloy layer having a high reflectance.
Further, according to the method of the related art, the pole tip 200 is formed by ion milling with a lower etching rate, and therefore etching process takes a long time, requiring a considerable time to finish processing of the pole tip 200. Such a tendency is not limited to formation of the pole tip 200, but the same applies to formation of the top pole 112 and other magnetic layers (such as the bottom shield layer 103, the bottom pole 107, and the like).